One of the uses of a fluid valve of the type to which the present invention relates is as a fuel injector for injecting a combustible fuel into a combustion engine. In the case of a spark-ignited, internal combustion engine for an automotive vehicle, the valve is typically under the control of an electronic control system and injects gasoline into the engine.
One of the chief reasons for using a fuel-injected engine is because of the ability to closely control the amount of fuel entering the engine. Close control over injected fuel is important for reasons of both fuel economy and exhaust emissions. When a fuel injector is closed, it should totally prevent fuel from leaking into the engine because such leakage can have undesired consequences. For example, even small amounts of leakage can adversely affect exhaust emissions in very significant ways. Certain countries now impose limits on the amounts of certain exhaust constituents that can be discharged to the atmosphere, and there is a trend toward making these limits even stricter. Accordingly, a commercially acceptable fuel injector is likely to have to comply with increasingly stringent limits on leakage.
Extremely costly manufacturing procedures could, of course, be invoked to insure precise surface finishes and fits of the cooperating parts by placing extremely small tolerances on the dimensions and surface finishes of the parts involved. Such activities would obviously increase the manufacturing costs, possibly to non-competitive prices for some companies. Alternate procedures that are less costly are therefore desirable.
The present invention relates to a new and unique method for reducing leakage in mass-produced fuel injectors of the type described at the beginning. The invention involves the inclusion of an additional step in the manufacturing process, but it eliminates the necessity for stricter tolerances on surface finish and part dimensions. Accordingly, manufacturing procedures that are presently in existence continue to enjoy vitality, and all that is needed to reduce leakage through the injector is the performance of what will be called for convenience a coining step. This coining step however does not involve the use of a coining die to coin a part; rather, it involves the application of axial compressive load to force the rounded distal end of the needle against the frusto-conical valve seat surface so that coining action occurs at an annular zone of surface contact between the two parts involved. The force application is preferably conducted in a particular manner so that the needle is neither irreversibly bent nor buckled by the coining step. This step is conducted during the manufacturing process so that neither the solenoid nor the spring which are parts of the operating mechanism in the completed injector has an influence on the result of the coining. Actual usage of the method of the invention has been found to to improve the yield of the mass-production process by approximately 10%, meaning that in a typical production run, that many more injectors will comply with applicable fuel leakage specifications when tested after assembly. This improvement reduces the number of injectors that have to be either re-worked or scrapped. Accordingly, the invention provides a significant improvement in the manufacturing process at the cost of only a single additional step. At that, the equipment needed to perform the additional step is neither extremely expensive nor complicated.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode presently contemplated for carrying out the invention.